The present invention is directed to methods and compositions for forming golf ball covers, cores and intermediate layers and a golf ball formed of said compositions having improved properties. The method comprises combining an ionomer and a polyamide-containing polymer to produce a novel compatible blend of polymeric materials used in forming, e.g., golf ball covers, and, more particularly, a golf ball comprising one or more layers formed from substantially compatibilizer-free blends of ionomers and polyamide-containing polymers.
Three-piece, wound balls with balata (trans-polyisoprene) covers are typically preferred by professional and low handicap amateur golfers. These balls provide a combination of distance, high spin rate, and control that is not available with an ionomer cover or in one-piece and two-piece balls. However, balata cuts easily, and lacks the durability required by the average golfer.
Two-piece golf balls, which are typically used by the average amateur golfer, provide a combination of durability and maximum distance that is not available with balata covered balls. These balls comprise a core, formed of a solid sphere which typically comprises a polybutadiene based compound, encased in an ionomer cover, such as SURLYN(copyright). Golf ball cover ionomers are, typically, copolymers of an olefin and an unsaturated carboxylic acid in which at least a portion of the carboxylic acid groups have been neutralized with a metal ion. These balls are extremely durable, have good shear resistance and are almost impossible to cut. However, the durability results from the hardness of the ionomer, which gives such balls a very hard xe2x80x9cfeelxe2x80x9d when struck with a golf club that many golfers find unacceptable.
Golf ball manufacturers have attempted to produce golf ball covers that provide the spin rate of balata with the cut resistance of an ionomer by forming blends of high hardness and low hardness ionomers, e.g., U.S. Pat. Nos. 4,884,814, 5,120,791, 5,324,783, 5,415,937 and 5,492,972. However, none of the disclosed ionomer blends have resulted in the ideal balance of carrying distance, coefficient of restitution, spin rate and initial velocity that would approach the highly-desirable playability of a balata covered golf ball.
Manufacturers have also attempted to form blends consisting essentially of hard ionomers with softer, nonionomer polymers to soften the golf ball and improve its feel and spin rate. However, this approach has proven to be difficult because the ionic character of ionomers imparts a highly polar nature to these materials. Therefore, ionomers and other non-ionic polymers, such as balata, and polyolefin homopolymers, copolymers, or terpolymers that do not contain ionic, acidic, basic, or other polar pendant groups, have not been successfully blended for use in golf ball covers. These mixtures often have poor mechanical properties such as inferior tensile strength, impact strength, and the like. Hence, the golf balls produced from these incompatible mixtures will have inferior golf ball properties such as poor durability and cut resistance on impact.
In light of the inferior properties imparted to golf balls by the ionomer and nonionomer polymer blends of the prior art, as described above, other approaches to forming such blends have been attempted by manufacturers. For example, U.S. Pat. Nos. 4,986,545, 5,098,105 and 5,359,000 all disclose compatible or miscible blends between ionomers and nonpolar polymers which have been modified by the addition of polar functionality. Compatibility is accomplished by imparting polar functionality to the nonionomer polymer through a reaction with maleic anhydride. Alternatively, a compatibilizer component has been added to provide or enhance the compatible nature of such blends; see, for example, U.S. Pat. Nos. 5,155,157 and 5,321,089 and Japanese patent application 6192512 A (1994). The compatibilizer material is often a block copolymer, where each block has an affinity for only one of the blend components to be compatibilized, or an epoxy containing compound. However, in each of these disclosures or publications, a costly chemical modification step or an added compatibilizer component is required to compatibilize a blend of one or more ionomers with a polymer that is otherwise incompatible with the ionomer. None of the above disclosures or publications teaches a compatible or miscible blend of an ionomer with a polyamide-containing polymer in the absence of a compatibilizing agent.
It is known in the polymer art that polyethylene-based ionomers may act as emulsifiers or compatibilizers when added to otherwise incompatible blends of a polyamide with a polyolefin. J. M. Willis et al., J. Materials Sci., 26:4742 (1991). For example, uncompatibilized polyamide/polyethylene blends are known to be immiscible or incompatible, that is, characterized by two distinct phases. However, they can be compatiblized by adding a polyethylene-based ionomer during melt blending. Blends of thermoplastics, including nylon, with ionomers having improved low temperature properties, such as flex-crack resistance, are the subject of U.S. Pat. No. 4,801,649 and European Patent Application A2 148,632. Furthermore, blends of nylon 6,6 and ionomer resins are known for their high toughness. (See: O. Olabisi, Encyclopedia of Chemical Technology, 3rd Edition, 18:474 (1982)). However, the use of polyamide-ionomer blends in golf ball compositions or in golf balls is not disclosed by these references.
U.S. Pat. No. 5,244,969 to Yamada discloses golf ball covers comprising a blend of two specific ethylene-acrylic acid copolymer ionomer resins and less than 20% by weight of a polyamide. Yamada does not claim or even disclose, however, a blend of a single ionomer resin and a polyamide.
U.S. Pat. No. 5,427,377 to Maruoka discloses reclaimed golf balls made by applying a thin skin of an ionomer resin optionally blended with a polyamide to resurface a golf ball which has been previously ground so that the dimples and damaged areas are removed. However, the reclaimed golf balls have inferior flying distance and durability compared to virgin golf balls.
Several patents disclose blends of polyamide elastomers and ionomers. For example, U.S. Pat. No. 4,858,924 to Saito et al. discloses the use of 3-35 wt % of a flexible resin, which can include a polyamide elastomer, blended with an ionomer for use as the cover of a golf ball. The cover blend is required to have a flexural modulus within the range of 21,000-64,000 psi (1500-4500 kg/cm2). The polyamide elastomer is said to be incompatible with the ionomer such that it forms a discrete phase dispersed in the ionomer. Saito et al. ""924 do not disclose any compatible polyamide-containing polymer and ionomer blends or any hardness requirements for any of the components or for the overall blend.
U.S. Pat. No. 4,919,434 to Saito discloses the use of a polyamide elastomer blended with an ionomer for use as the inner or outer cover of a golf ball. Described only as elastomeric, the polyamide elastomer material is said to have a low flexural modulus and hardness. However, the exact chemical composition or structure of the polyamide elastomer is not disclosed. When blended with an ionomer, the polyamide elastomer-ionomer blend outer cover layer is said to have a flexural modulus of 28,000-71,000 psi (2000-5000 kg/cm2). However, Saito ""434 is silent on the hardness characteristics of the blends and of their components.
U.S. Pat. No. 5,556,098 to Higuchi et al. discloses the use of a three-layer golf ball with a soft middle layer composed of a blend of a polyamide elastomer and an ionomer, such that the JIS C hardness of the blend is less than 80. The exact chemical composition or structure of the polyamide elastomer is not disclosed other than that it is said to be a thermoplastic elastomer. Higuchi et al. are silent on the flexural modulus characteristics of these blends and of their components.
It should be noted that none of the above publications on polyamide elastomers and their ionomer blends disclose blends of polyamide/ionomer or copolyamide/ionomer.
Block copoly(amide-ether)s, available commercially as PEBAX(copyright) from Elf Atochem S.A., have been disclosed as cover compositions for golf balls, for example, by Deleens et al. in U.S. Pat. No. 4,234,184. These materials are formed by reacting a polyamide that has been end-capped to form an xcex1,xcfx89-dicarboxylic copolyamide with a dihydroxy-terminated polyether. Deleens et al. also provide for the possibility of blends containing the block copoly(amide-ether), but only with a minor proportion of a compatible polymer with a melting point and hardness comparable to the block copolymer.
Cores for multi-piece golf balls, as well as one-piece balls, comprised of blends of an ionomer and a block copoly(amide-ether) are disclosed in U.K. Patent Application GB 2,164,342 A. However, this reference is silent on the hardness and flexural modulus characteristics of the blends or their components.
U.S. Pat. No. 5,253,871 to Viollaz discloses the use of at least 10% of a block copoly(amide-ether), optionally blended with an ionomer, for use as the middle layer of a three-layer golf ball. The Shore D hardness of the block copolymer is said to be within the range of 30-40 Shore D hardness while the corresponding hardness of the ionomer component is said to be between 55-65 Shore D. The overall hardness of the middle layer is said to range from 20-50 Shore D. The cover may also be a block copoly(amide-ether) and ionomer blend but its overall hardness must be greater than that of the adjacent middle layer. However, Viollaz is silent on the flexural modulus characteristics of the blends or their components.
It should be noted that none of the above publications on block copoly(amide-ether)s and their ionomer blends disclose blends of polyamide/ionomer or copolyamide/ionomer.
UK patent application GB 2299999 A discloses a three layer golf ball with a soft cover layer and a hard intermediate layer. The intermediate layer is said to contain at least 5% by weight of a high-rigidity polyamide resin, optionally blended with an ionomer. Preferred polyamides are said to have a stiffness or bending modulus of 140 to 252 kpsi. The bending modulus of the intermediate layer composition is said to range from 56,000 to 112,000 psi, preferably 70,000 to 112,000 psi, while its Shore D hardness is said to range from 65 to 90. The cover layer of the three layer golf ball is said to comprise ionomer resin with a stiffness of 14,000 to 35,000 psi and Shore D hardness of 56 to 64.
It should be noted that this publication does not disclose a blend of copolyamide/ionomer, nor disclose a blend of block polyamide copolymer including main chain polyether blocks/ionomer present in a cover layer, nor does it disclose a blend of polyamide/ionomer present in an intermediate layer that is softer than the cover layer.
None of the blended compositions described above provides the combination of durability and distance that is provided by two-piece golf balls with ionomer covers and the high spin rate and control that is available with three-piece, wound golf balls with balata covers. Therefore, there remains a need for a method of making golf ball cores, intermediate layers and covers that provides for the blending of thermoplastic ionomers with other polymers without the need for compatibilizers which complicate and raise the cost of such a process, to provide one-piece, two-piece and/or multi-layer golf balls with the durability and distance of a SURLYN(copyright) covered two-piece ball and the feel, click, and control of a balata covered three-piece ball. The present invention provides such a method, and produces such a product.
One embodiment of the present invention relates to a golf ball comprising a cover and a core, said cover comprising at least one layer, wherein an outermost layer of said cover is formed of a composition which comprises a substantially compatibilizer-free blend of about 10 wt. % to about 80 wt. % of at least one ionomer and about 90 wt. % to about 20 wt. % of at least one polyamide homopolymer or polyamide copolymer, wherein the polyamide polymer is selected from the group consisting of polyamide homopolymers, polyamide copolymers and mixtures thereof.
A further embodiment of the present invention relates to a golf ball comprising a cover and a core, said cover comprising at least one layer, wherein an outermost layer of said cover is formed of a composition which comprises a substantially compatibilizer-free blend of about 10 wt. % to about 80 wt. % of at least one ionomer and about 90 wt. % to about 20 wt. % of at least one polyamide polymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks. Some examples of block polyamide copolymers that would be excluded under the proviso are block copoly(amide-ether), block copoly(amide-ester-ether) and block copoly(amide-urethane-ether). However, block copoly(amide-ester), block copoly(amide-urethane-ester), block copoly(amide-thioether), block copoly(amide-ester-thioether) and block copoly(amide-urethane-thioether) for example, would not be excluded under the proviso since they have no main chain polyether blocks.
Polyamide polymers useful in the invention include, but are not limited to, polyamide homopolymers, polyamide copolymers, block polyamide copolymers and mixtures thereof. Preferred polyamide homopolymers include nylon 6, nylon 11, nylon 12, nylon 4,6, nylon 6,6, nylon 6,9, nylon 6,10, nylon 6,12 and mixtures thereof. The more preferred polyamide homopolymers are nylon 11 and nylon 12. The flexural modulus of the polyamide homopolymer is at least about 50,000 psi.
Preferred polyamide copolymers include nylon 6/6,6, nylon 6,6/6,10, nylon 6/6,T wherein T represents terephthalic acid, nylon 6/6,6/6,10 and mixtures thereof. The flexural modulus of the polyamide copolymer is at least about 50,000 psi.
Preferred block polyamide copolymers include main-chain blocks selected from the group consisting of polyester, polyurethane, xcex1,xcfx89-hydroxybutadiene oligomer, hydrogenated xcex1,xcfx89-hydroxybutadiene oligomer, wherein the degree of hydrogenation may be partial or substantially complete, and mixtures thereof.
More preferably, the flexural modulus of the polyamide polymer is from at least about 75,000 psi to about 500,000 psi.
Ionomers useful in the invention include but are not limited to olefin, polyester, copoly(ether-ester), copoly(ester-ester), polyamide, polyether, polyurethane, polyacrylate, polystyrene, styrene-butadiene-styrene (also known as SBS), styrene-(hydrogenated butadiene)-styrene wherein the degree of hydrogenation may be partial or substantially complete (also known as SEBS), and polycarbonate homopolymer, copolymer and block copolymer ionomers, and mixtures thereof.
The preferred ionomers comprise a copolymer of an olefin and an xcex1,xcex2-ethylenically unsaturated carboxylic acid in an amount of between about 5 wt. % to about 30 wt. %, where at least a portion of the carboxylic acid groups are neutralized with a metal ion. In more preferred ionomers, the olefin is ethylene, the xcex1,xcex2-ethylenically unsaturated carboxylic acid is acrylic or methacrylic acid, and the metal ion is selected from the group consisting of zinc, sodium, magnesium, manganese, calcium, lithium and potassium. In the most preferred ionomers, the carboxylic acid is present to the extent of about 10% to about 20% by weight and the metal ion is zinc. The flexural modulus of the ionomer is at least about 1,000 psi, preferably from at least about 1,000 psi to about 150,000 psi.
The present invention also relates to a golf ball comprising a cover and a core, where the cover is formed of a composition comprising a substantially compatibilizer-free blend of about 10 wt. % to about 80 wt. % of an ionomer resin, where the flexural modulus of the ionomer is at least about 1,000 psi, and about 90 wt. % to about 20 wt. % of at least one polyamide polymer, where the flexural modulus of the polyamide component is at least about 75,000 psi, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks.
Preferably, the golf ball of the invention comprises a cover and a core, with the cover formed of a composition which is a substantially compatibilizer-free blend of about 15 wt. % to about 75 wt. % of an ionomer resin, where the ionomer comprises a copolymer of ethylene and about 10% to about 20% by weight of acrylic or methacrylic acid, where at least a portion of the carboxylic acid groups are neutralized with zinc and where the flexural modulus of the ionomer is from at least about 1,000 psi to about 150,000 psi, and about 85 wt. % to about 25 wt. % of nylon 11 or nylon 12, where the flexural modulus of the nylon 11 or nylon 12 is from at least about 50,000 psi to about 500,000 psi.
An alternate embodiment of the present invention is directed to a golf ball comprising a cover layer, a core layer and at least one intermediate layer interposed there-between, wherein at least one of said layers is formed of a composition comprising a substantially compatibilizer-free blend of about 10 wt. % to about 80 wt. % of at least one ionomer resin and about 90 wt. % to about 20 wt. % of at least one polyamide polymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks and further that the cover consists essentially of at least one material selected from the group consisting of nonionomer polymer materials and non-olefin ionomers.
A further alternate embodiment of the present invention is directed to a golf ball comprising a cover and a core, said cover comprising at least one layer, wherein an outermost cover layer is formed of a composition which consists essentially of about 5 wt. % to about 95 wt. % of an ionomer and about 95 wt. % to about 5 wt. % of at least one polyamide polymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks.
An additional embodiment of the present invention is a golf ball comprising a cover layer, a core layer and at least one intermediate layer interposed there-between, wherein at least one of said layers consists essentially of about 0 wt. % to about 99 wt. % of at least one ionomer resin and about 100 wt. % to about 1 wt. % of at least one polyamide polymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks and further that the cover consists essentially of at least one material selected from the group consisting of nonionomer polymer materials and non-olefin ionomers.
The invention also relates to a method of making a golf ball, which comprises forming a golf ball core, forming a substantially compatibilizer-free blend comprising about 10 wt. % to about 80 wt. % of at least one ionomer resin and about 90 wt. % to about 20 wt. % of at least one polyamide polymer, with the proviso that the polyamide polymer is not a block polyamide copolymer comprising main-chain polyether blocks, and forming an outermost cover layer upon said ball by molding the blend around the golf ball core.